Responses of inspiratory neurons of the dorsal respiratory group to stimulation of expiratory muscle and vagal afferents

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In decerebrate, paralyzed and ventilated cats, we monitored the intracellular responses of 30 inspiratory neurons of the dorsal respiratory group (DRG) to stimulation of vagal and expiratory muscle (internal intercostal and abdominal) afferents. We hypothesized that the inhibitory effects of stimulation of expiratory muscle afferents, previously reported, would block the excitatory responses of inspiratory neurons of the DRG to vagal stimulation. Although prolonged stimulus trains to expiratory muscle afferents caused respiratory phase-switching, single shocks or short trains elicited no responses in 17 bulbospinal neurons, excitatory responses in 6, and inhibitory responses in 2. Of the 4 propriobulbar neurons tested, 2 had inhibitory responses and 2 did not respond. In only 2 neurons, both bulbospinal, did conditioning stimuli to expiratory muscle afferents block or reduce the excitatory effects of vagal stimulation. These results suggest that interaction of vagal and expiratory muscle afferents, which might account for the absence of a change in inspiratory duration despite increased vagal afferent feedback at elevated end-expiratory lung volumes, does not occur within the DRG.